MICROSCOPIC plankton more commonly known as ''sea sparkle'' has given Lake Victoria on the Gippsland Lakes an electric blue trim.

The bioluminescence is caused by a chemical reaction inside the micro-organism, which gives off the light when disturbed by movement in the water.

The natural glow generated by the plankton, Noctiluca scintillans, was photographed by astrophotographer Phil Hart between January 11 and 16. ''Because it reacts to movement, you can see fish swimming about in the water, you can see ropes tied to boats moving about and if you throw stones or look at the small waves lapping at the shoreline you can see it,'' Mr Hart said. ''But if the waves are too big then the water is too disturbed and you don't see it as much.''

Bioluminescence is appearing again in the Gippsland Lakes. Photo: Phil Hart

Areas where Noctiluca scintillans is present are much more attractive at night - by day the water appears little more than cloudy. At high levels the water may appear to have a reddish scum on the surface. But at night the electric blue steals the show.

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''If you've seen it once, you keep trying to see it again,'' he said. ''It seems an unnatural colour for what we normally consider the natural world.''

Perran Cook, from Monash University's faculty of science, said floods last June created ideal conditions for the microscopic plankton, which measure a tenth of a millimetre in size.

While the micro-organism is in the water year round, it is only noticeable when it blooms. The floods washed nutrients into the water system, which prompted a boom in phytoplankton - the primary food source for Noctiluca scintillans.

''These guys are now cleaning them up,'' Dr Cook said. ''They're like the vacuum cleaner of the phytoplankton in the water column.''

A biogeochemist, Dr Cook said the plankton could adjust their buoyancy allowing them to exist on the surface and deeper in the water column.

He said unlike blue-green algae outbreaks, Noctiluca scintillans posed no risk to health. However he said a diet of nitrogen-rich phytoplankton produced high levels of ammonia, causing odours.

Bioluminescence is not uncommon in nature - it appears in fungi and fireflies. However, Dr Cook said there was no definitive explanation for why the microscopic plankton luminesced when disturbed. Theories range from it being a defence mechanism to scare predators to a camouflage technique.

''It sounds counter-intuitive,'' he said. ''But imagine if you are looking up from below in the water, instead of looking at a dark silhouette against a moon and star-lit sky, it becomes less visible.''